fmars-06-00495 August 16, 2019 Time: 18:14 # 1

ORIGINAL RESEARCH published: 20 August 2019 doi: 10.3389/fmars.2019.00495

Recent Eruptions Between 2012 and 2018 Discovered at West Mata Submarine Volcano (NE Lau Basin, SW Pacific) and Characterized by New Ship, AUV, and ROV Data

William W. Chadwick Jr.1*, Kenneth H. Rubin2, Susan G. Merle3, Andra M. Bobbitt3, Tom Kwasnitschka4 and Robert W. Embley3

1 NOAA Pacific Marine Environmental Laboratory, Newport, OR, United States, 2 Department of Earth Sciences, University of Hawai’i at Manoa,¯ Honolulu, HI, United States, 3 CIMRS, Oregon State University, Newport, OR, United States, 4 GEOMAR, Helmholtz Centre for Ocean Research, Kiel, Germany

West Mata is a submarine volcano located in the SW Pacific Ocean between Fiji and Samoa in the NE Lau Basin. West Mata was discovered to be actively erupting at its summit in September 2008 and May 2009. Water-column chemistry and hydrophone Edited by: data suggest it was probably continuously active until early 2011. Subsequent repeated Cristina Gambi, Marche Polytechnic University, Italy bathymetric surveys of West Mata have shown that it changed to a style of frequent Reviewed by: but intermittent eruptions away from the summit since then. We present new data Paraskevi Nomikou, from ship-based bathymetric surveys, high-resolution bathymetry from an autonomous National and Kapodistrian University underwater vehicle, and observations from remotely operated vehicle dives that of Athens, Greece Simon James Barker, document four additional eruptions between 2012 and 2018. Three of those eruptions Victoria University of Wellington, occurred between September 2012 and March 2016; one near the summit on the upper New Zealand ENE rift, a second on the NE flank away from any rift zone, and a third at the NE base *Correspondence: William W. Chadwick Jr. of the volcano. The latter intruded a sill into a basin with thick sediments, uplifted them, [email protected] and then extruded lava onto the seafloor around them. The most recent of the four eruptions occurred between March 2016 and November 2017 along the middle ENE rift Specialty section: This article was submitted to zone and produced pillow lava flows with a shingled morphology and tephra as well as Deep-Sea Environments and Ecology, clastic debris that mantled the SE slope. ROV dive observations show that the shallower a section of the journal recent eruptions at West Mata include a substantial pyroclastic component, based Frontiers in Marine Science on thick (>1 m) tephra deposits near eruptive vents. The deepest eruption sites lack Received: 02 April 2019 Accepted: 22 July 2019 these near-vent tephra deposits, suggesting that pyroclastic activity is minimal below Published: 20 August 2019 ∼2500 mbsl. The multibeam sonar re-surveys constrain the timing, thickness, area, Citation: morphology, and volume of the new eruptions. The cumulative erupted volume since Chadwick WW Jr, Rubin KH, Merle SG, Bobbitt AM, 1996 suggests that eruptions at West Mata are volume-predictable with an average Kwasnitschka T and Embley RW eruption rate of 7.8 × 106 m3/yr. This relatively low magma supply rate and the high (2019) Recent Eruptions Between frequency of eruptions (every 1–2 years) suggests that the magma reservoir at West 2012 and 2018 Discovered at West Mata Submarine Volcano (NE Lau Mata is relatively small. With its frequent activity, West Mata continues to be an ideal Basin, SW Pacific) and Characterized natural laboratory for the study of submarine volcanic eruptions. by New Ship, AUV, and ROV Data. Front. Mar. Sci. 6:495. Keywords: submarine volcanoes, submarine eruptions, seafloor mapping, bathymetry changes, multibeam sonar doi: 10.3389/fmars.2019.00495 surveying, lava flow morphology, pyroclastic activity, autonomous and remotely operated underwater vehicle

Frontiers in Marine Science | www.frontiersin.org 1 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 2

Chadwick et al. Recent Eruptions at West Mata Volcano

INTRODUCTION The observations also provide information about the character of individual eruptions at different depths, because they span the We learn the most about active volcanic processes by directly entire volcano from the summit to abyssal depths (Figure 2). We observing them, a fact that motivates the establishment of show that the recent eruptions define a linear trend in erupted observatories at Earth’s most active volcanoes. Eruptions that volume with time, which has implications for the magma supply, occur on land have obvious manifestations, making them easy the volume of magma storage within the volcano, and the future targets for enhanced observation and study, but detecting and behavior of the volcano. observing volcanic eruptions in the deep sea is much more difficult (Rubin et al., 2012), despite the fact that most of Earth’s volcanic output occurs in the oceans (Crisp, 1984). PREVIOUS WORK Frequently active submarine volcanoes provide a rare and valuable opportunity to learn about the underwater processes West Mata first gained attention in November 2008 during associated with individual eruptions as well as how a submarine a regional hydrographic survey that discovered an intense volcano’s activity evolves with time (Staudigel et al., 2006; Watts hydrothermal plume over the summit with high levels of et al., 2012; Schnur et al., 2017; Allen et al., 2018; Wilcock et al., hydrogen and shards of volcanic glass, suggesting it was actively 2018). West Mata is of special interest because it is an excellent erupting at the time (Resing et al., 2011; Baumberger et al., 2014). example of such a site. This led to a rapid-response expedition 6 months later in May West Mata is a frequently active submarine volcano with a 2009 with ROV Jason (Resing et al., 2011) that found two active summit depth at ∼1200 meters below sea level (mbsl) and a base eruptive vents on the north side of the summit ridge, named at nearly 3000 mbsl, located in the extensional NE Lau Basin Hades and Prometheus. The eruptive activity was continuous between Fiji and Samoa in the SW Pacific Ocean (Figure 1). It is at moderate to low effusion rates, and was characterized by one of only two places on Earth where active submarine eruptions explosive bursts that produced both pillow lavas and pyroclasts, have been directly observed in the deep sea (>500 mbsl depth) especially when large bubbles of magmatic gases up to ∼1 m in (Resing et al., 2011; Rubin et al., 2012). It is also by far the deepest diameter (presumably SO2, CO2,H2O) were expelled from the since the other site is NW Rota-1 Seamount in the Mariana arc, vent (Resing et al., 2011). which has a summit depth of 517 mbsl (Embley et al., 2006; During that same expedition in May 2009, the summit and rift Chadwick et al., 2008, 2012; Deardorff et al., 2011; Schnur et al., zones were mapped at high-resolution (1 m) with the MBARI 2017). West Mata is also unique because it is the only known AUV D. Allan B. (Clague et al., 2011; Clague, 2015), revealing site where lava of boninite composition is being erupted in a the setting of the Hades and Prometheus eruptive vents within modern tectonic setting, a composition often associated with embayments of the summit ridge on the upper north slope of the nascent inter-oceanic subduction (Resing et al., 2011; Rubin et al., volcano. The high-resolution AUV bathymetry also highlighted 2018). West Mata is the largest of nine volcanoes with similar the contrast in morphology between the smooth north and south morphology and composition, comprising the “Mata Group,” all slopes of the volcano, which are covered with volcaniclastic debris elongate cones with roughly parallel rift zones that are oriented shed from vents near the summit, and the hummocky lava flows in a WSW-ENE direction (Figure 1), suggesting a regional evident on the ENE and WSW rift zones. The rift zone flows have structural control (Clague et al., 2011; Rubin et al., 2018). a distinctive morphology with flat tops and steep sides and are The Mata Group volcanoes lie in a “rear-arc” tectonic setting, typically arranged in a shingled arrangement along the sloping between the Tonga volcanic arc to the east, and the NE Lau back- rift zone axis, locally modified by landslides. Clague et al. (2011) arc spreading center to the west, and in-board of the nearly 90◦ also compared the first ship-based bathymetric survey at West bend at the northern terminus of the Tonga trench, where it Mata in 1996 to later ones collected in 2008–2010 and found transitions into a plate boundary transform zone (Figure 1). The large depth changes at the summit (up to 88 m shallower) and NE Lau Basin hosts the world’s highest subduction rates (Bevis on north flank (up to 96 m shallower), suggesting that eruptive et al., 1995) and the fastest opening back-arc basin (Zellmer and activity from the summit vents had been dominant for more Taylor, 2001), which creates an extraordinary concentration and than a decade and had produced thick volcaniclastic deposits on diversity of submarine volcanism in the area (Embley and Rubin, the north flank. 2018; Rubin et al., 2018) and also hosts an extraordinary number Additional evidence that the eruptive activity directly obser- of active hydrothermal vent sites (Baker et al., 2019). ved during the brief ROV dives in May 2009 was continuous This paper presents new results from West Mata including and prolonged for months to years comes from local and depth changes between repeated bathymetric surveys from ships, regional hydrophone studies, radiometric dating, and repeated high-resolution mapping from autonomous underwater vehicles hydrothermal plume measurements in the water column over the (AUVs), and visual observations of the seafloor from remotely volcano. A moored hydrophone deployed ∼48 km SW of West operated vehicles (ROVs). The new data reveal and characterize Mata recorded the sounds of continuous but variable eruptive six eruptions at West Mata (Figure 2), a collapse pit at the activity at West Mata from January to May 2009 (Resing et al., summit, and a landslide scar just east of the summit that all 2011). During the May 2009 ROV dives, a portable hydrophone occurred after eruptive activity was first observed at the summit characterized from close range the eruptive activity at Hades in May 2009 (Resing et al., 2011; Embley et al., 2014). These and Prometheus, which was continuous during the several days new observations show that the eruptive style at West Mata of recordings (Dziak et al., 2015). A regional hydrophone array changed from continuous to episodic during this time period. in the Lau Basin ∼650 km to the SSW recorded sustained

Frontiers in Marine Science | www.frontiersin.org 2 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 3

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 1 | Regional map of the NE Lau Basin, located between Fiji and Samoa (inset), showing West Mata submarine volcano, between the NE Lau back-arc Spreading Center to the west and the Tofua volcanic arc to the east.

low-level activity in the direction of West Mata between January landslides were detected on the north flank of West Mata by 2009 and April 2010 (Bohnenstiehl et al., 2014). Another local the local moored hydrophones between December 2009 and May hydrophone array was moored 5–15 km away from the summit 2010 (Caplan-Auerbach et al., 2014). Ship-based CTD casts over from December 2009 to August 2011 and recorded continuous the summit in November 2008, May 2009, April/May 2010, and eruptive activity until late 2010, when it began to decline and September 2012 showed a gradual decrease in the strength of eventually stopped by February 2011 (Embley et al., 2014; Dziak chemical and particle signals in the hydrothermal plume above et al., 2015). Radiometric dating of lavas collected at or near the summit of West Mata during this time period, consistent with the summit in 2009 and 2012 using short-lived 210Po-210Pb the hydrophone data (Baumberger et al., 2014). disequilibrium confirmed that effusive volcanism spanned at least ROV dives in September 2012 confirmed that West Mata was April 2007 to December 2010 (Embley et al., 2014). no longer erupting continuously from the summit vents (Embley During the period of continuous eruptive activity, turbidity et al., 2014). Instead, a pit crater ∼200 m wide and ∼100 m sensors on one of the hydrophone moorings and on conductivity, deep had formed at the former location of Hades vent. Later temperature, depth (CTD) instruments during infrequent ship- analysis of additional repeated ship-based bathymetric surveys based vertical hydrographic casts showed evidence for occasional from 1996 to 2012 (Figure 2) revealed the first evidence for mass-wasting events down the flanks of West Mata (Dziak episodic eruptive activity on the rift zones (Embley et al., 2014). et al., 2015; Walker et al., under review1). Similarly, submarine Here, we build on those results with the first direct observations of recent eruption sites away from the summit at West Mata from AUV and ROV dives, as well as new evidence for four 1Walker, S. L., Baker, E. T., Lupton, J. E., and Resing, J. A. (under review). Patterns of fine ash dispersal related to volcanic activity at West Mata volcano, NE Lau additional episodic eruption sites on and near the rift zones Basin. Front. Mar. Sci. between 2012 and 2018.

Frontiers in Marine Science | www.frontiersin.org 3 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 4

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 2 | Map of West Mata showing areas where depth changes have been found by repeated bathymetric surveys between 1996 and 2018, documenting recent eruption sites. Those from 1996 to 2012 are from Clague et al. (2011) and Embley et al. (2014); those after 2012 are new (orange and red areas, see legend). The depth changes shown in white are several grouped together within a longer time window (2009–2012) than the time constraints on individual sites (see Embley et al., 2014). The blue areas are negative depth changes from a summit collapse and landslide. Numbers indicate eruption sites discussed in detail in this paper.

MATERIALS AND METHODS and in November 2017 (Table 1). We use the positive depth changes between bathymetric surveys to calculate the thicknesses, The main method we use for documenting recent eruptions areas, and volumes of erupted material at each site (Table 2). at West Mata is identifying significant depth changes between We have not re-calculated the volumes reported by Embley repeated ship-based multibeam sonar bathymetric surveys. The et al. (2014) for the depth changes before 2012. For those volcano has been mapped nine times between 1996 and 2018, after 2012, we calculate the areas and volumes of change using with eight of those since 2008 (Table 1 and Figure 3). The ArcMap GIS software by subtracting one bathymetric grid first survey in 1996 was collected with a lower resolution from another within a polygon that was manually drawn to sonar system and before reliable GPS navigation, so it is isolate the area of significant depth change. We do not use notably lower in quality and comparisons with it have higher the AUV bathymetry for the volume calculations because the uncertainty [as discussed by Clague et al. (2011) and Embley AUV surveys do not cover all the eruption sites and so the ship et al. (2014)]. Nevertheless, all the surveys since 2008 are of data provide a more uniform and consistent way of comparing relatively high quality and we generally can use a threshold multiple events. to identify significant depth changes of ±10 m. Still, not Most of the new data presented in this paper were collected all depth changes above this threshold are real, but false during a two-leg expedition on R/V Falkor to the NE Lau positives can be eliminated by comparing with visual ground Basin between 10 November and 18 December 2017 (FK171110). truth from submersibles and/or whether they make geologic The first leg included dives with AUV Sentry to collect high- sense, based on their location and morphology. The timing resolution (1 m) bathymetry (at 70 m altitude) and near- of the eruptions associated with each confirmed area of bottom photo surveys (at 5 m altitude) of selected areas. depth change is constrained by the dates of the before-and- Four of six AUV Sentry dives were made at West Mata after bathymetric surveys. All the bathymetric data at West (dives 457, 458, 460, and 463) and the first three collected Mata were processed using MB-System software (Caress and useful data with its Reson 7125 (200 kHz) multibeam sonar Chayes, 2016) and were gridded at a 25-m grid-cell spacing (Merle et al., 2018a); unfortunately the multibeam sonar for this analysis. malfunctioned during the later dive. Where they overlap, the In this paper, we focus on the depth changes discovered 2017 AUV Sentry bathymetry can be compared with the 2009 since those documented by Embley et al. (2014) by using the survey by the MBARI AUV D. Allan B. (Clague et al., 2011; two most recent ship-based bathymetric surveys in March 2016 Clague, 2015).

Frontiers in Marine Science | www.frontiersin.org 4 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 5

Chadwick et al. Recent Eruptions at West Mata Volcano

TABLE 1 | Multibeam sonar bathymetric surveys at West Mata volcano.

Month-Year Vessel/vehicle Cruise ID Chief Scientist(s) Sonar system

June-1996 R/V Melville BMRG08MV S. Bloomer/D. Wright Seabeam2000 November-2008 R/V Thompson TN227 J. Lupton EM300 May-2009 R/V Thompson TN234 J. Resing/R. Embley EM300 May-2009 AUV D. Allan B. TN234 D. Clague/D. Caress Reson 7125 May-2010 R/V Kilo Moana KM1008 J. Resing EM122 December-2010 R/V Kilo Moana KM1024 K. Rubin/R. Embley EM122 November-2011 R/V Kilo Moana KM1129a F. Martinez EM122 September-2012 R/V Revelle RR1211 J. Resing/R. Embley EM122 March-2016 R/V Falkor FK160320 T. Kwasnitschka EM302 November-2017 R/V Falkor FK171110 K. Rubin/W. Chadwick EM302 November-2017 AUV Sentry FK171110 K. Rubin/W. Chadwick Reson 7125

FIGURE 3 | The timeline showing the timing of multibeam sonar bathymetric surveys (MB), AUV and ROV dives in 2009, 2012, and 2017, and the transition in eruptive style from continuous summit activity to episodic rift zone eruptions (represented by red “E’s” below the timeline).

TABLE 2 | Estimates of the thicknesses, areas, and volumes of recent eruption sites at West Mata based on depth changes between ship-based bathymetric surveys.

Bathymetric survey Geographic area Mean depth Maximum depth Area of depth Volume of depth Site name comparison (mo/years) and depth change in meters change in meters change (x 106 m2) change (x 106 m3)

Eruption sites newly identified by this study Site 1 March 2016 – November 2017 ENE Rift @ 1500 m 26.6 71 0.6 14 Site 2 November 2011 – March 2016 ENE Rift @ 1300 m 38.6 93 0.530 13.8 Site 3 November 2011 – March 2016 NE flank @ 2400 m 27.2 57 0.250 6.7 Site 4 November 2011 – March 2016 NE Base @ 2700 m 29.2 64 0.730 17.1 Areas previously identified by Embley et al. (2014) Site 5 May 2010 – November 2011 WSW Rift @ 2900 m 26.2 63 0.61 16 Site 6 May 1996 – November 2008 WSW Rift @ 2700 m 53.5 101 0.22 12

During the second leg of the R/V Falkor expedition, dives (Merle et al., 2018b). Other results from this expedition are were made with ROV SuBastian, and 7 of 21 dives were made described in Rubin et al. (2018), Walker et al., under review2, at West Mata (S85–S88, S93, S95, and S103) to make visual and Baker et al. (2019). observations and collect samples at most of the recent eruption sites documented by bathymetric depth changes. Both cruise 2Walker, S. L., Baker, E. T., Lupton, J. E., and Resing, J. A. (under review). Patterns legs collected ship-based multibeam bathymetry at West Mata of fine ash dispersal related to volcanic activity at West Mata volcano, NE Lau and the surrounding area with the ship’s EM302 sonar system Basin. Front. Mar. Sci.

Frontiers in Marine Science | www.frontiersin.org 5 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 6

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 4 | Broad-view maps of eruption site #1, on the middle ENE rift zone of West Mata (see Figure 2) showing (a) pre-eruption MBARI AUV bathymetry from 2009, (b) post-eruption Sentry AUV bathymetry from 2017, and (c) positive depth differences between ship-based surveys in 2016 and 2017 overlain on 2017 AUV bathymetry (see Table 2). Black outlines enclose the site #1 eruption deposits. In this and subsequent figures, the pre-eruption AUV bathymetry was collected in May 2009 by the MBARI AUV D. Allan B. (Clague et al., 2011; Clague, 2015), and the post-eruption AUV bathymetry is from surveys in November 2017 with AUV Sentry (Merle et al., 2018a).

Frontiers in Marine Science | www.frontiersin.org 6 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 7

Chadwick et al. Recent Eruptions at West Mata Volcano

RESULTS the rift zone, within the headwall of a previous landslide on the SE side of the rift (Figure 4). The depth changes between ship- The summary timeline in Figure 3 shows the timing of all the based bathymetric surveys in 2016 and 2017 were greatest near ship-based multibeam sonar bathymetric surveys at West Mata the eruptive vents where lava flows accumulated (up to 71 m between 1996–2018 (black arrows labeled with “MB”), as well thick). Smaller positive depth changes (up to 34 m) extend at least as the years with ROV and AUV dives, and how the new data 2.2 km downslope, where the smooth texture in the post-eruption reported here fit into the longer time-series of observations. AUV bathymetry and photographs from AUV Sentry show that Remarkably, there is evidence for eruptive activity between these are volcaniclastic deposits. The area between the thick lava almost every bathymetric survey, except between the surveys flows and the thinner fragmental deposits downslope had small less than a year apart in 2008 and 2009, and those in 2011 negative depth changes (up to 5–10 m, not shown in Figure 4c), and 2012, which showed no change. The red “E’s” in Figure 3 suggesting that some scouring occurred as the volcaniclastic denote episodic eruptions on the rift zones, whose timing is material moved downslope. The total area enclosing the eruptive constrained by the bathymetric surveys. The arrows at the bottom deposits (black outline in Figure 4) is 0.60 × 106 m2, and their highlight the major transition that occurred in early 2011 when total volume is 14.0 × 106 m3 (Table 2). the continuous eruptive activity at the summit ended (Embley A zoomed-in view of the upper part of the eruption site et al., 2014). At about the same time, the summit collapsed and a (Figure 5) shows that the new lava flows form a series of flat- landslide occurred on the SE flank with a headwall just east of the topped or slightly domed plateaus with steep margins, arranged summit (blue arrows in Figure 3). Since 2011, all the eruptions in an overlapping, shingle-like or stepped pattern, descending to at West Mata have been episodic eruptions on the rift zones. the ENE in the direction parallel to the rift axis. Adjacent to the Although this was clearly a major change in eruptive behavior, rift, there are five somewhat equi-dimensional overlapping lava note also that there was some overlap in time between the plateaus, each 100–150 m across with downward steps of 20–30 m continuous and episodic activity. The first episodic rift eruption between them (Figure 5b). Below these are a series of lava was documented between May 2009 and May 2010 (Embley et al., benches that become progressively smaller and less well-defined 2014), and there was an even earlier one sometime between the with distance downslope, eventually merging into a hummocky 1996 and 2008 surveys (although it’s possible that event occurred lobe of pillow lava that extends 600 m from the rift (Figure 5b). before the continuous activity began). The steep downslope margins of the lava benches and plateaus In this section, we focus on six recent eruption sites: the are constructional in some places, but are cut by landslide scarps four discovered on and near the ENE rift zone from the two in others (for example along the scalloped southern edge of most recent bathymetric surveys in 2016 and 2017 (sites #1–4 the upper-most lava plateaus in Figure 5b). Because the lava in Figure 2), and two previously identified on and near the plateaus are relatively flat-topped but were built outward from WSW rift zone by Embley et al. (2014) where we have new the rift on a steeply descending slope, each lava plateau is data to ground-truth previous interpretations (#5–6 in Figure 2). actually wedge-shaped in cross-section; the bathymetric depth- We describe the eruption sites roughly from youngest to oldest, changes between the AUV surveys show that the lava plateaus are starting with the 2016–2017 site, then the three 2012–2016 thinnest on their upslope edges and thickest on their downslope eruption sites, and then the older two sites on the WSW rift. edges (Figure 5c). This is consistent with their mechanism of However, for the 2012–2016 sites, note that their relative ages are formation being similar to that of perched lava ponds on land, unknown (the positioning of the “E’s” in Figure 3 between 2012 as proposed by Clague et al. (2011), in which the relatively flat and 2016 is arbitrary), and we therefore proceed from shallowest upper surface of a flow lobe is maintained behind a levee that to deepest among those three sites. Note also that to compute is constructed from overflows at the edge of the impounded depth differences at the 2012–2016 eruption sites (Table 2), we lava flow. In this interpretation, the levee grows upward along have chosen to compare the 2016 survey to the 2011 survey rather with the upper surface of the ponded lava flow. In any case, this than the one in 2012 because the latter is noisier. So even though “shingled lava plateau” morphology is very common along both we show depth changes between the 2011 and 2016 surveys in the rift zones of West Mata. figures and tables, we know that the timing of those depth changes Visual observations of the 2016–2017 eruptive deposits were is constrained in time between 2012 and 2016. made during ROV SuBastian dives S86 and S103 in December 2017 (Figure 5d). The hummocky lobe of pillow lavas on the lower reaches of the eruption site lies on a moderate slope Site 1: The 2016–2017 Eruption on the and has a thin dusting of tephra (Figure 6a). Further upslope, Middle ENE Rift at 1500 mbsl the steep margins of the lava plateaus and lava benches are The most recent known eruption at West Mata occurred between constructional in some places, formed by near-vertical intact March 2016 and November 2017 and was discovered during the pillow tubes (Figure 6b), and in other places are vertical cliffs FK171110 expedition on R/V Falkor. This eruption was located of truncated pillows (Figure 6c), where they have been cut by on the middle part of the ENE rift zone, between 1.0 and 1.5 km landslides. Below the landslide headwalls are ramps of talus east of, and about 300 m below the summit (Figure 2). Figure 4 made up of pillow fragments (Figure 6d). In contrast, the upper shows the before-and-after AUV bathymetry at the eruption site. surfaces of the lava plateaus (near the eruptive vents) consist Comparing the AUV bathymetry from 2009 and 2017 shows of pillow lavas that are deeply buried by coarse volcanic tephra that the eruptive vents were located along the southern edge of (Figure 6e). The thickness of the tephra appears to be 1–2 m,

Frontiers in Marine Science | www.frontiersin.org 7 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 8

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 5 | Close-up maps of eruption site #1 showing (a) pre-eruption MBARI AUV bathymetry from 2009, (b) post-eruption Sentry AUV bathymetry from 2017, (c) positive depth differences between the AUV surveys (after the 2017 Sentry AUV grid was co-registered by shifting it 8 m east and 16 m south), and (d) trackline of SuBastian ROV dive S86 (white line) on post-eruption Sentry AUV bathymetry, with locations of images in Figure 6 (white numbered circles). Part of SuBastian ROV dive S103 also crossed this area, but is not shown in (d). In (c) note that shingled lava plateaus thicken downslope away from the rift zone (see text for discussion). Black outlines enclose the site #1 eruption deposits and mark the edges of individual shingled lava plateaus.

based on the fact that most pillows are buried and only the Figure 8 shows a smaller area near the summit and eruptive largest poke above the tephra (Figure 6f). The tephra layer vent in more detail. The 2009–2017 time period between the is pock-marked by numerous bowl-shaped, circular pits, about two AUV surveys captures changes due to several events during 0.5–1 m across (Figures 6e,f) that apparently formed when tephra that span. A new pit crater formed at the summit between “drained” downward into empty cavities among the underlying December 2010 and November 2011 when the area that included pillow lavas. Locally, these circular pits have accumulated small the Hades and Prometheus vents collapsed (Figures 8a,b), yellow flocculent particles of microbial mat (Figure 6f), which perhaps associated with the end of continuous eruptive activity apparently originally formed on the upper surface of the tephra, (Embley et al., 2014). The crater has a roughly oval outline, but were subsequently dislodged and transported into the pits by about 200 × 100 m wide and 100 m deep, with the long axis bottom currents. Locally, a mosaic of white and yellow microbial parallel the rift zones (Figure 8c). The crater rim on the NW mat still blanketed the tephra in some areas (Figure 6g). We edge displays elongated pillow lava lobes, probably originally measured a temperature of 5◦C (a few degrees above ambient) fed from Hades vent but now truncated by the collapse (see in one such area with the ROV’s temperature probe as it was Figures 10c,d of Embley et al., 2014). The deepest part of the pushed downward about 10 cm into the tephra deposit. The crater (1290 mbls), just 25 m W of the former location of steps between the lava plateaus are constructional levees of nearly Hades vent, hosted diffuse venting of clear shimmering fluids vertical pillow lava tubes, and were relatively unburied by tephra up to 22◦C in 2017. The former location of Hades is now because of their steepness (Figure 6h). a high-standing pinnacle within the crater, and the former location of Prometheus vent is along the eastern rim of the crater (Figure 8c), where it abuts the east-facing headwall Site 2: The 2012–2016 Eruption East of of the landslide that also occurred between December 2010 the Summit at 1300 mbsl and November 2011 (Embley et al., 2014). The high-standing The first of the three eruption sites constrained in time between areas remaining between Hades and Prometheus may have 2012 and 2016 is located on the uppermost ENE rift zone just east escaped significant collapse (Figure 8), perhaps because the of the summit (Figure 7). The shallowest point at the eruptive former vent areas are underlain by relatively massive intrusive vent is 1255 mbsl and the deepest extent of the erupted deposits rocks. These are also areas of continuing extensive diffuse is at least 1950 mbsl on both the SE and N flanks of the rift hydrothermal venting. zone. The area and volume of the 2011–2016 depth differences The 2012–2016 eruptive vent is 70 m below and 300 m east from this eruption are 0.53 × 106 m2 and 13.8 × 106 m3, of the summit, and was clearly centered within the headwall respectively (Table 2). scar of the 2010–2011 landslide (labeled in Figure 8c), where

Frontiers in Marine Science | www.frontiersin.org 8 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 9

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 6 | Images of eruption site #1 from ROV SuBastian dive S86. All are 2016–2017 eruption products. Numbers in parentheses are time of photo in GMT and horizontal scale. See Figure 5d for photo locations. (a) Pillow lavas on the slope below the rift zone (19:17:22, 5 m). (b) Nearly vertical cliff face of intact pillow lavas (20:09:42, 4 m). (c) Nearly vertical cliff of truncated pillows on the headwall of a landslide scarp (20:52:51, 4 m). (d) Talus with pillow fragments below a landslide scarp (20:48:50, 10 m). (e) Tephra-covered pillow lavas on a shingled lava plateau near the eruptive fissures, with circular pits containing yellow microbial floc in the distance (21:40:18, 10 m). (f) Closer view of collapse pit in tephra deposit with yellow microbial floc (bottom) and large partially buried pillow at center (21:47:06, 4 m). (g) Colorful microbial mats growing on tephra completely burying pillow lavas on a shingled lava plateau near the eruptive fissures (23:41:48, 6 m). (h) Exposed tubular pillow lavas on the steep step between shingled lava plateaus (22:27:47, 3 m).

Frontiers in Marine Science | www.frontiersin.org 9 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 10

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 7 | Broad-view maps of eruption site #2, just east of the summit of West Mata (see Figure 2) showing (a) pre-eruption MBARI AUV bathymetry from 2009, (b) post-eruption Sentry AUV bathymetry from 2017, and (c) positive depth differences between ship-based surveys in 2012 and 2016 (Table 2). Black outlines enclose the site #2 eruption deposits. White dots show locations of Hades and Prometheus eruptive vents in May 2009.

Frontiers in Marine Science | www.frontiersin.org 10 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 11

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 8 | Close-up maps of eruption site #2 showing (a) pre-eruption MBARI AUV bathymetry from 2009, (b) post-eruption Sentry AUV bathymetry from 2017, (c) geological interpretation on 2017 AUV bathymetry and (d) tracklines of SuBastian ROV dives S85, S87, and S103 (white lines) on post-eruption Sentry AUV bathymetry, with locations of images in Figure 9 (white numbered circles). Thick white arrows in (c) indicate lava flow directions from eruptive vent; thick black hachured lines are crater rims or landslide headwalls. Thin black outlines enclose the site #2 eruption deposits. White dots show locations of Hades and Prometheus eruptive vents in May 2009.

the new lavas are shallowest and the largest depth differences lava flows are themselves cut by east-facing landslide scarps on (up to 93 m) form a circular bullseye pattern (Figure 7c). the south side of the rift zone (Figure 8c). These appear to From there, it appears that lava and clastic debris were first have formed both during and after the eruption since there deposited downslope to the east >1 km, more or less down are some pillow-lava deposits on the slope below the landslide the axis of the previous landslide chute, but as the eruption headwall (Figure 8c). built a constructional mound over the vent, it gained enough ROV SuBastian dives S85, S87, and S103 were made elevation to also feed pillow lava flows down the northern flank in this area (Figure 8d) and showed that the near-vent of the rift zone (Figure 8c). The thickest accumulation of lava deposits are pillow lavas that form a steep flow front on the north side of the rift (67 m) is mid-way down the flank where they abut the 2010–2011 landslide headwall west (Figure 7c). The morphology of the downslope eruptive deposits of the eruptive vent (Figures 9a,b). As the eruptive vent are notably different on the two sides of the rift zone; on the SE was approached, thick deposits of tephra were observed side they are smooth, whereas those on the N side are hummocky mantling the pillows (Figure 9c), and were locally covered (Figure 7b). This contrast indicates the early deposits on the by white and yellow microbial mats (Figure 9d). Near the SE side are mainly volcaniclastic, suggesting more explosive or eruptive vent spatter-like deposits were observed (Figure 9e) higher-effusion rate activity at the beginning of the eruption, providing more evidence for a pyroclastic component to the whereas those on the north are intact pillow lava flows, suggesting eruption. Diffuse venting of clear hydrothermal fluids was the later phase of the eruption developed a more stable lava observed over a large area that was colonized by abundant distribution system from the vent to the north slope, perhaps vent animals including shrimp, squat lobsters, and polychete at a lower effusion rate. On the axis of the rift zone, the depth worms (Figure 9f). The edge of the pillow mound that differences are relatively thin (4–11 m, Figure 7c), but it is had been cut by a landslide was marked by truncated clear there is new lava there because of different morphology pillows, some of which were hollow with drained-out interiors in the 2017 AUV bathymetry (Figure 8b) and our ROV dive (Figure 9g). Within the landslide headwall, cross-sections of observations. Nevertheless, there are some older high-standing the pillow mound could be seen in near-vertical outcrops features in that area that did not get buried by the new lava oriented downslope, showing layer upon layer of elongate flows. The 2017 AUV bathymetry also shows that the 2012–2016 pillows (Figure 9h).

Frontiers in Marine Science | www.frontiersin.org 11 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 12

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 9 | Images of eruption site #2 from ROV SuBastian dives S85, S87, and S103. All show 2012–2016 eruption products. Numbers in parentheses are dive number, time of photo in GMT and horizontal scale. See Figure 8d for photo locations. (a) 2012–2016 flow front at left against the 2010–2011 landslide headwall at right (S85, 01:52:19, 10 m). (b) Close up of pillow lavas on flow front (S85, 01:58:13, 3 m). (c) Tephra partly burying pillows close to eruptive vent (S85, 02:59:14, 5 m). (d) Tephra with white and yellow microbial mats mantling pillows (S85, 03:18:12, 3 m). (e) Near-vent spatter deposits with yellow hydrothermal sediment (S85, 02:50:48, 5 m). (f) Hydrothermal vent shrimp swarm at active diffuse vent with shimmering cloudy water (S87, 03:19:25, 3 m). (g) Hollow drained-out pillow where new lavas are cut by landslide scarp (S103, 02:42:53, 1.5 m). (h) Cross-section of stack of elongate pillow lavas cut by landslide scarp, with downslope direction to the left (S85, 02:45:15, 10 m).

Frontiers in Marine Science | www.frontiersin.org 12 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 13

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 10 | Maps of eruption site #3, the pillow ridge on the NE flank of West Mata (see Figure 2) showing (a) post-eruption Sentry AUV bathymetry from 2017, (b) positive depth differences between ship-based surveys in 2012 and 2016 (Table 2), (c) trackline of SuBastian ROV dive S93 (white line) on Sentry AUV bathymetry, with locations of images in Figure 11 (white numbered circles), and (d) close-up showing hummocky intact pillow lavas on the gentler upslope side of the ridge contrasting with smooth talus ramps below landslide scarps on the steeper downslope side. Black outlines enclose the site #3 eruption deposits.

Site 3: The 2012–2016 Eruption on ridge (Figure 10c). The hummocky areas of lesser depth change the NE Flank at 2400 mbsl that extend as fingers downslope from the thick pillow ridge The second recent eruption site constrained in time between (Figures 10a,b) are thinner (<10 m) flows of pillow lava. These 2012 and 2016 is located on the NE flank of West Mata were apparently produced in an early phase of the eruption when (Figure 2). It is unusual because it is well off the ENE rift lava was fed from the fissure at a slightly higher effusion rate zone and the smooth morphology of the rest of the NE flank before it slowed and became localized at discrete points along (from volcaniclastic debris produced upslope) makes it clear that the eruptive fissure to produce the thicker pillow mounds. The eruptions do not occur here often. This site was beyond the thinnest margins of the flow field (probably the earliest flows) are coverage of the 2009 AUV survey, so we do not have high- covered with rippled deposits of tephra (Figure 11a), suggesting resolution bathymetry before the eruption, but pre-2012 ship- downslope transport by turbidity currents during a pyroclastic based bathymetry shows a featureless slope. The post-eruption phase of this eruption. Deposits of tephra are ubiquitous on AUV survey in 2017 (Figure 10a) shows that the eruption the thicker pillow lavas, but are less obvious on steeper slopes. produced a linear ridge of coalesced pillow lava mounds that is On the upslope sides of the pillow mounds, the constructional rotated ∼26◦clockwise to the radial direction from the summit. slopes are nearly vertical (Figure 11b) with elongate pillow lava The orientation of the pillow ridge may have been influenced tubes that remained intact all the way to the flow margins by basement structure nearby, as it is parallel to an older (Figure 11c). In contrast, on the unbuttressed downslope sides sedimented and tectonized ridge NE of the volcano (Figure 2). of the pillow mounds, the pillow lavas did not remain intact and Lava was apparently erupted along a fissure ∼1 km long, formed vertical cliffs of truncated pillows in the upper reaches extending from 2365 to 2635 mbsl on a slope averaging 15–20◦. (Figure 11d) and aprons of pillow talus below (Figure 11e). This The depth differences between ship-based surveys (Figure 10b) contrast in morphology is evident in the high-resolution AUV show the maximum thickness of the lavas is 57 m, the area bathymetry with intact hummocky flows on the upslope side of erupted material is 0.25 × 106 m2, and the volume is of the pillow mounds, and cliffs with smooth ramps of pillow 6.7 × 106 m3 (Table 2). talus below on the downslope side (Figure 10d). On the flatter ROV SuBastian dive S93 traversed from the NE base of tops of the pillow mounds, a thin dusting of yellow sediment the volcano upslope along the length of the 2012–2016 pillow (Figure 11f) and abundant polychete worms were evidence for

Frontiers in Marine Science | www.frontiersin.org 13 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 14

Chadwick et al. Recent Eruptions at West Mata Volcano

low-level diffuse hydrothermal venting. The tops of the upper- in the AUV bathymetry (Figure 12c). Tumuli are formed by most pillow mounds are marked by small pit craters (Figure 10a) internal pressure within inflating lava flows that pushes up the with overhanging edges (Figure 11g), indicating that some of the overlying solidified crust in a trap-door fashion on either side mounds had a core of molten lava that drained out and collapsed of an axial crack (Walker, 1991; Appelgate and Embley, 1992). during the later stages of the eruption. Locally, the tops of the These tumuli are the shallowest features on the 2012–2016 lava pillow mounds were covered with pyroclastic tephra deposits up flows (Figure 13e), and are in line with the long-axis of the to several 10s of cm thick, with occasional collapse pits as seen at large dome of uplifted sediment, so may overlie the eruptive site #1 (Figure 11h). vents for the lava flows. From there, pillow lavas flowed mostly to the west and then northward, around the uplifted sediment, Site 4: The 2012–2016 Eruption at but also flowed a shorter distance to the east (Figure 12c). the NE Base at 2650 mbsl North of the tumuli, the young lavas lap up onto the uplifted Figure 13f The third of the recent eruption sites between 2012 and 2016 is dome of sediment ( ). The longitudinal cracks on also in an unusual location, at the NE base of the volcano in a the sediment dome that are evident in the AUV bathymetry basin 1–2 km north of the axis of the deepest part of the ENE appear as broad swales, 10–40 m wide and 3–8 m deep, with rift zone (Figure 2). Before the eruption, ship-based bathymetry little or no stratigraphy evident in their walls in the southern Figure 13g showed a broad oval basin in the area, 1–1.5 km across and half of the dome ( ). However, in the center of the relatively flat at ∼2700 mbsl. The 2009 AUV survey did not uplifted sediment dome, where the swales are wider and deeper, extend over this site. After the eruption, ship-based bathymetry stratigraphy was exposed in the side walls and yellow microbial shows positive depth changes throughout the basin up to 64 m mat showed evidence of local diffuse hydrothermal discharge 6 2 (Figure 13h). At that site the ROV’s temperature probe measured (Figure 12b), covering an area of 0.73 × 10 m , and amounting ◦ to a volume change of 17.1 × 106 m3 (Table 2). a temperature of 15 C within the sediments, apparently residual The AUV bathymetric survey over this site in 2017 was heat from magma intruded below. particularly revealing (Figure 12a). The high-resolution map showed that much of the eastern half of the basin appeared to Site 5: The 2010–2011 Eruption on the be uplifted sediments (Figure 12c), smooth seafloor that had Deep WSW Rift at 2950 mbsl been domed upward and cut by numerous longitudinal spreading cracks, like those on a loaf of bread when it comes out of the oven In December 2017, we also made ROV SuBastian dive S95 on two Figure 2 (suggesting a nickname we used for the site: “the muffin”). The older areas of depth change (sites #5–6, ) documented uplifted sediments were surrounded by hummocky seafloor that on the deep WSW rift zone by Embley et al. (2014). These are appeared to be young lava flows that flowed around the uplift the first visual observations of these eruption sites and provide without a clearly defined eruptive vent (Figure 12c). ground-truth that these depth changes are indeed associated Observations during ROV SuBastian dive S88 confirmed with young lava flows. They also give additional information on this interpretation (Figure 12d). The edges of the young lava the character of recent eruptions at West Mata, particularly at flow are marked by thin pillow lobes over the surrounding the deepest depths. sediment, with occasional larger higher-standing pillows that The first of the two eruption sites (site #5) visited on ROV Figure 14c have undergone inflation, expansion, and cracking (Figure 13a). dive S95 ( ) is constrained in time between May 2010 + The new lavas and the surrounding sediments are both covered and November 2011 (time period IV V of Embley et al., with volcaniclastic-rich ripple marks that form a zebra-striped 2014). Because this area is beyond the obvious morphological polygonal pattern with darker tephra on the ripple crests and extent of the rift zone, it was not mapped during the 2009 lighter-colored pelagic sediment in the troughs (Figures 13a–d). AUV bathymetric survey. We attempted to map the site with The volcaniclastic-rich sediment is about 1–2 cm thick on the AUV Sentry in 2017, but unfortunately the multibeam sonar young lavas and appears to be evenly distributed throughout failed on this dive (#463) and so no high-resolution bathymetry the area (on both sediments and lava), with no locally thicker exists for this site (although a photo survey was collected by Figure 14a accumulations observed. Because of this, we interpret that the Sentry). The post-eruption ship bathymetry ( ) and Figure 14b majority of volcaniclastic material is not juvenile (syn-eruptive). the 2010–2011 depth differences ( ) show that the lava Instead, we hypothesize that it was probably deposited by flows that were erupted cover an area of 1300 by 700 m across × 6 2 turbidity currents from further upslope after the eruption, such (0.61 10 m ), are up to 63 m thick along a ridge oriented ENE- as those documented by Walker et al., under review3. This WSW in the southern half of the flow field (probably overlying × 6 3 interpretation implies that pyroclastic tephra was not a major the eruptive fissure), and have a total volume of 16.0 10 m component of the eruptive products at this site, the deepest of (Embley et al., 2014). the four most recent eruption sites (2650–2700 mbsl). The lava flow field is composed entirely of intact lava flows, A series of sinuous tumulus structures, up to 125 m long and with no landslide scarps or talus ramps, due to the relatively 5 m high are located between the two areas of uplifted sediment low slopes that existed in this area before the eruption. The lavas have a fine dusting of light-colored sediment on them. The northern margin of the lava flow field has broad pillow 3Walker, S. L., Baker, E. T., Lupton, J. E., and Resing, J. A. (under review). Patterns of fine ash dispersal related to volcanic activity at West Mata volcano, NE Lau lava lobes (Figure 15a), which grade locally into lobate and Basin. Front. Mar. Sci. ropy sheet flow morphology, in some areas with very flat

Frontiers in Marine Science | www.frontiersin.org 14 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 15

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 11 | Images of eruption site #3 from ROV SuBastian dive S93. All show 2012–2016 eruption products. Numbers in parentheses are time of photo in GMT and horizontal scale. See Figure 10c for photo locations. (a) Rippled tephra-rich sediment deposited on thin pillow lava flow margin downslope of pillow ridge (21:26:05, 5 m). (b) Nearly vertical constructional slope on upslope side of pillow ridge (23:19:35, 5 m). (c) Margin of young lavas (at right) on upslope side of pillow ridge (22:48:40, 4 m). (d) Truncated pillows in landslide scarp on steeper downslope side of pillow ridge (01:39:25, 8 m). (e) Ramp of pillow talus below landslide scarp on downslope side of pillow ridge (01:33:28, 10 m). (f) Thin yellow hydrothermal sediment and tephra on lavas at top of pillow ridge (00:32:02, 3 m). (g) Overhanging rim of collapse pit at top of pillow mound due to drain-out of molten interior (02:33:15, 4 m). (h) Tephra deposit mantling pillow lavas at upslope end of pillow ridge (02:48:08, 5 m).

Frontiers in Marine Science | www.frontiersin.org 15 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 16

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 12 | Maps of eruption site #4, at the NE base of West Mata (see Figure 2) showing (a) post-eruption Sentry AUV bathymetry from 2017, (b) positive depth differences between ship-based surveys in 2012 and 2016 (Table 2), (c) geological interpretation on 2017 AUV bathymetry, and (d) trackline of SuBastian ROV dive S88 (white line) on Sentry AUV bathymetry, with locations of images in Figure 13 (white numbered circles). In (d) note that the navigation for this dive was considerably noisier than for others on this expedition due to problems with the acoustic tracking system on R/V Falkor. Black outlines enclose the site #4 eruption deposits; white outlines in (c) delineate uplifted sediments and inset shows detail of tumuli structures in young lava flows.

upper surfaces that are locally uplifted into tumuli structures is a post-eruption survey in this case (Figure 14a). The depth (Figure 15b), providing evidence for flow inflation. Further differences between the ship-based surveys in 1996 and 2008 are south, long tubular pillows mantle the northern slope of the ENE- up to 101 m (Figure 14b), with an area of 0.22 × 106 m2 and a WSW eruptive ridge (Figure 15c). Near the crest of that ridge, volume of 12.0 × 106 m3 (Embley et al., 2014). the pillows again broadened on the gentler slope, and sheet- The morphology of this site is considerably different than like lava morphology with local drainback were observed near the previous one, mostly because the eruption occurred on an apparent eruptive fissure (Figure 15d). On the north side of the much steeper slopes on the rift zone. Consequently, the the flow field where it sloped down and abutted a sedimented flow field is composed of repeated sequences of gently sloping ridge, tephra-rich ripple marks in the sediment were oriented intact pillow lavas on the crests of constructional mounds perpendicular to the axis of the rift zone with volcaniclastic (Figure 15f), surrounded by steep slopes of truncated pillows accumulations on the lee sides (Figure 15e), consistent with on the margins of the mounds (Figure 15g), where the sediment transport from further upslope by bottom currents. pillows have broken apart and formed talus ramps below No significant accumulations of tephra were observed on the (Figure 15h), which in turn lap onto the next constructional 2010–2011 lava flows. This is the deepest of the recent eruption pillow mound downslope (Figure 14). Again, no significant sites (2890–2975 mbsl). tephra accumulations were observed on these lava flows. Neither site #5 or #6 displayed any evidence of active hydrothermal venting (shimmering water, microbial mats, vent animals, etc.), Site 6: The 1996–2008 Eruption on the but local accumulations of yellow hydrothermal sediment showed Deep WSW Rift at 2750 mbsl that it had occurred previously. On the same ROV dive (SuBastian S95) we also traversed the eruption site that is just upslope on the WSW rift zone (site #6, Figure 2), which was discovered and constrained between the DISCUSSION 1996–2008 bathymetric surveys by Embley et al. (2014) (their time period I). In contrast to the previous site, this eruption was Comparison of Recent Eruption Sites on the deepest morphologic expression of the WSW rift zone The most recent ROV dive observations show that all four of and so was included in the 2009 AUV bathymetric survey, which the most recent eruption sites at West Mata (#1–4; 2012–2018)

Frontiers in Marine Science | www.frontiersin.org 16 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 17

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 13 | Images of eruption site #4 from ROV SuBastian dive S88. Numbers in parentheses are time of photo in GMT and horizontal scale. See Figure 12d for photo locations. (a) Margin of 2012–2016 pillow lavas at right (21:32:51, 8 m). (b) Closer view of 2012–2016 pillow lavas (21:11:48, 3 m). (c) Lava lobe with rippled volcaniclastic-rich sediment on surface (21:05:22, 2 m). (d) Close up of rippled volcaniclastic-rich sediment (21:47:26, 0.5 m). (e) Uplifted lava at tumulus structure (23:18:54, 8 m). (f) 2012–2016 pillow lava (left) lapped up on south edge of uplifted sediment dome at right (23:50:51, 3 m). (g) Broad swale (left) and edge of extension crack (right) in southern part of uplifted sediment dome (00:32:58, 10 m). (h) Yellow microbial mat growing on edge of extensional crack with stratigraphy in central part of uplifted sediment dome (00:35:18, 5 m).

Frontiers in Marine Science | www.frontiersin.org 17 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 18

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 14 | Map of eruption sites #5 (left) and #6 (right), at the SW base of West Mata (see Figure 2) showing (a) post-site-#5-eruption ship-based bathymetry (left) overlain with post-site-#6-eruption MBARI AUV bathymetry from 2009 (right), (b) positive depth differences between ship-based surveys (2010–2011 at left, 1996–2008 at right, see Table 2), and (c) trackline of SuBastian ROV dive S95 (white line) on post-eruption bathymetry, with locations of images in Figure 15 (white numbered circles). Note that the navigation for this dive was considerably noisier than for others on this expedition due to problems with the acoustic tracking system on R/V Falkor. Black outlines enclose the site #5 and #6 eruption deposits.

have deposits that were still warm and cooling in December 2017 and polychetes), microbial mats, and elevated temperatures (from months to perhaps up to 5 years after they were erupted), measured in tephra or sediments just below the surface. In exhibiting some combination of diffuse hydrothermal venting addition, diffuse hydrothermal venting was observed all around colonized by vent animals (particularly shrimp, squat lobsters, the summit, both inside and outside of Hades Crater, despite

Frontiers in Marine Science | www.frontiersin.org 18 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 19

Chadwick et al. Recent Eruptions at West Mata Volcano

FIGURE 15 | Images of eruption sites #5 (2010–2011) and #6 (1996–2008) from ROV SuBastian dive S95. Numbers in parentheses are time of photo in GMT and horizontal scale. See Figure 14c for photo locations. (a) Broad lobes of 2010–2011 lava near northern flow margin (20:34:50, 5 m). (b) Uplifted sheet lava in tumulus structure near northern 2010–2011 flow margin (22:21:14, 5 m). (c) elongate pillows on north slope of 2010–2011 pillow ridge (23:14:48, 8 m). (d) Eruptive fissure with lava drain-out at crest of 2010–2011 pillow ridge (01:24:04, 8 m). (e) Volcaniclastic-rich sediment ripples at southern margin of 2010–2011 pillow ridge, oriented perpendicular to the downslope direction (00:05:08, 5 m). (f) Crest of 1996–2008 pillow lava mound with intact lavas (03:35:11, 3 m). (g) Landslide scarp of truncated 1996–2008 pillows on downslope edge of pillow mound (03:31:13, 5 m). (h) Pillow talus below landslide scarp in 1996–2008 lavas (02:39:27, 5 m).

Frontiers in Marine Science | www.frontiersin.org 19 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 20

Chadwick et al. Recent Eruptions at West Mata Volcano

the end of eruptive activity there by early 2011. This implies the landslides occurred. These processes produce ramps of pillow that active diffuse hydrothermal activity exists more or less talus and finer clastic debris downslope. In places, late-stage continuously at West Mata due to the heat delivered or mined pillow lava flows were also emplaced within the co-eruption from recent eruption sites and the relatively short recurrence landslide chutes, providing additional evidence for the overlap of interval between eruptions. This is important for the continuity volcanic construction and mass-wasting processes at the eruption of local vent-dependent ecosystems. In contrast, no evidence sites on steep slopes. for continued venting was observed at the two older eruption In contrast, eruption sites on gentler slopes at “off-rift” sites sites visited by ROV in 2017 (#5–6; 1996–2011), suggesting that produced a different set of eruption deposits and morphologies. venting usually does not persist for longer than 5–10 years at These sites include #4 and #5, which are both located beyond eruption sites on the rift zones. the morphological expression of West Mata’s rift zones on The ROV dive observations also show that there is a variation flatter terrain off the main edifice (Figure 2). At site #4, in eruptive character with depth at West Mata. The shallower based on the distinctive morphologies evident in the AUV recent eruption sites (sites #1, #2, and to some extent #3) have bathymetry, we interpret that magma first intruded into the very significant deposits of tephra near the eruptive vents (up to sedimented basin as a sill that thickened and uplifted the 1–2 m thick and extending for 100s of m laterally), showing overlying sediments. Eventually, continued intrusion allowed that violent degassing and lava fragmentation are common. We the magma to reach the surface, probably along faults on envision this eruptive behavior as similar to the spectacular video the edge of the uplifted sediment, and lava then erupted observations of explosive activity at the summit vents during onto the seafloor and flowed around the domed uplift. This ROV Jason dives in May 2009 (Resing et al., 2011; Rubin et al., is similar to the scenario envisioned for intrusions/eruptions 2012). In addition, there is some evidence that the eruptive style into sediment on the Escanaba Trough of the Gorda Ridge evolves during a single eruption, with a progression from more (NE Pacific) (Denlinger and Holmes, 1994; Morton and Fox, pyroclastic to more effusive with time. On the other hand, at site 1994; Zierenberg et al., 2013) and for several locations on #1 a thick tephra deposit overlies pillow lavas, so it appears that the Pescadero and Tamayo transform faults in the Gulf of pyroclastic activity continued throughout the eruption there. In California (Clague et al., 2018). At site #5, lava flows erupted contrast, the deeper recent eruption sites (sites #4, #5, and #6) onto the gently sloping seafloor adjacent to the rift zone do not have locally thick, near-vent deposits of tephra, suggesting and spread out to form low-relief sheet flows. Both sites that little tephra is produced by eruptions at West Mata below a produced broad lava flows with evidence of inflation and depth of about 2500 m. Nevertheless, we did observe tephra on morphologies ranging from pillows to lobate flows to ropy the recently erupted lava flows, but these deeper deposits were lava, with local tumulus structures that formed due to internal evenly distributed (on and off the new flows) and heavily rippled, pressure within the molten interior of the sheet-like flows. suggesting the tephra was transported from areas further upslope Co-eruption landslides or auto-brecciation and talus formation and deposited by episodic turbidite-like bottom currents that were not components of these eruptions on gentler slopes. move fragmental material downslope, as envisioned by Walker These two eruption sites are also the deepest documented at et al., under review4. West Mata and show that eruptions can take place beyond The observations also demonstrate that the map-scale the obvious morphological limits of the rift zones at the morphology of individual eruption deposits is highly dependent base of the volcano. on the underlying slope of each site. For example, the “on-rift” Eruption site #3, the pillow ridge on the NE flank of West eruption sites that are located on relatively steep slopes (sites #1 Mata, is somewhere in between these end-members, in that it has & 2, and to some extent site #6) are characterized by pillow lava evidence for both constructional pillow lava mounds and local flows that are locally emplaced as “shingled lava plateaus,” which co-eruption mass-wasting on the steeper downslope side of the form inflated lava flows with slightly domed upper surfaces that pillow ridge. On the other hand, it clearly did not form within are impounded by levees of nearly vertical elongate pillow lavas at a previous landslide scar nor on one of West Mata’s rift zones, their downslope edges, like perched lava-ponds on land. At sites and indeed its location is hard to explain. One possibility is that #1 and #2 there is clear evidence that the recent eruptive vents if it was the last of the three eruptions that occurred between were localized within the headwall scars of previous landslides 2012 and 2016, then because the previous two (sites #2 and #4) on the steep margins of the rift zone. We know the landslide at would have presumably been fed by dikes that intruded along the site #2 occurred between December 2010 and November 2011, ENE rift zone, perhaps the compressional stresses across the rift whereas at site #1 the slide scar had been there since the first from those intrusions would not have had enough time to relax bathymetric survey in 1996. There is also ample evidence for so that the next dike intrusion was forced to take a different path landslides occurring during or soon after eruptions where the to the surface. Instead, a dike intruded outward from beneath recent lava flows are cut by scarps exposing truncated pillows the summit in a direction close to radial, but outside of the rift in nearly vertical cliffs with local evidence for lava drain-out, zone. Another possibility is that this eruption site was controlled showing that parts of the flow interiors were still molten when by deeper crustal structure related to the older ridge NE of the volcano. In any case, this must be a relatively rare event based on West Mata’s morphology and the lack of other similar examples. 4Walker, S. L., Baker, E. T., Lupton, J. E., and Resing, J. A. (under review). Patterns of fine ash dispersal related to volcanic activity at West Mata volcano, NE Lau It is clear that most eruptions at West Mata occur either at the Basin. Front. Mar. Sci. summit or along the rift zones.

Frontiers in Marine Science | www.frontiersin.org 20 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 21

Chadwick et al. Recent Eruptions at West Mata Volcano

Common Patterns in Submarine Effusive Volcanism Despite the differences in tectonic setting and magma composition, the characteristics of the recent eruption deposits at West Mata volcano are notably similar to the results from studies at many other recent submarine eruption sites. In particular, our observations are quite similar to those at other basaltic submarine volcanoes where high-resolution AUV bathymetry and ROV dives allow direct comparisons of map-scale morphology of lava flows and interpretation of their emplacement. Commonalities include the construction of thick hummocky flows of pillow lava with evidence of molten interiors and steep flanks locally modified by co-eruption landslides forming aprons of talus, as well as evidence for inflation of more fluid lava flows on gentler FIGURE 16 | Cumulative erupted volume at West Mata vs. time, based on slopes, and intrusion and eruption processes in sedimented volumes of depth change between nine repeated ship-based bathymetric surveys listed in Table 1. Volumes are from Table 2 and Embley et al. (2014) basins. Such comparable AUV/ROV datasets include those from and are plotted at the time they were discovered (the second of each pair of the Juan de Fuca and the Gorda spreading ridges and the Alarcon surveys). Trend is remarkably linear and implies volume-predictable eruptive Rise in the NE Pacific (Caress et al., 2012; Chadwick et al., 2013, behavior in which the volume of the next eruption is predictable from the time 2016; Yeo et al., 2013; Zierenberg et al., 2013; Clague et al., since the previous one. 2014, 2017, 2018), the East Pacific Rise (White et al., 2000, 2002; Fornari et al., 2004; Soule et al., 2007; Fundis et al., 2010; Klein collapse, due to magma withdrawal from shallow levels beneath et al., 2013; Deschamps et al., 2014), and the Galapagos spreading the summit to the deep WSW rift zone, similar to the recent ridge (Haymon et al., 2008; White et al., 2008; McClinton activity at Kilauea volcano, Hawaii (Neal et al., 2019). However, et al., 2013). The combined results of these high-resolution this connection cannot be demonstrated conclusively because geological studies show that the effusive eruptive processes we the time constraints on the two events are slightly different. describe here are not unique to West Mata, but are widespread Hades crater formed between December 2010 and November and common to mafic submarine eruptions in diverse tectonic 2011, whereas the site #5 eruption occurred between May 2010 settings, demonstrating their importance on a global scale and and November 2011, but the difference is only because the site a convergence of scientific understanding about submarine #5 eruption was beyond the coverage of the December 2010 effusive volcanism. On the other hand, the significant deposits of multibeam survey (Embley et al., 2014). pyroclastic tephra at the shallower eruption sites at West Mata In any case, the transition from continuous to episodic are quite unusual, and probably reflect the high volatile content eruptions overlapped in time and it is likely that the onset of of its boninite parent magma (Resing et al., 2011; Rubin et al., activity on the rift zones destabilized the conditions that allowed 2018). These tephra deposits and their implications will be the continuous eruption at the summit. The first three episodic subject of future studies. events between 2009 and 2011 were along the WSW rift zone This study shows that the combination of high-resolution (while activity at the summit was waning), and subsequent events bathymetry with visual observations of the seafloor and a time- have all been along the ENE rift zone between 2012 and 2018 series of repeat mapping surveys can provide insights into the (after the summit activity had stopped). Over longer periods of emplacement processes of effusive submarine eruptions. The time, this distributed volcanism along the rift zones may be the documentation of multiple eruptive events over a significant norm at West Mata, intermixed with occasional extended periods depth range illustrates a variety of eruption styles, products, and of eruptive activity at the summit. Nevertheless, it is remarkable environments. Observations over an extended period of time that over the last 22 years the locations of eruptive activity have reveal the spatial and temporal evolution of volcanic activity, can spanned the entire volcano from the deepest parts of both rift constrain rates of magma supply, and show how construction and zones, to the summit, to locations in between, and even off the mass wasting events are closely linked. rifts such as on the NE flank. This suggests that when dikes are intruded at West Mata they tend to seek regions within the Recent Eruption History at West Mata edifice with relatively low compressive stress, which are likely If we consider the history of known eruptions at West Mata since areas that have not experienced the most recent intrusions and 1996 (Figure 3), the most significant change in the character eruptions (Acocella and Neri, 2009). This is similar to the way in of that activity was the shift from continuous eruptive activity which individual dike intrusions were spatially distributed along at the summit to episodic eruptions on the rift zones that different parts of the extensional plate boundary during the 1975– occurred around early 2011 (although admittedly we know far 1984 Krafla rifting episode in Iceland (Björnsson et al., 1979; less about the activity before 2008 than afterward). This change Björnsson, 1985; Buck et al., 2006). was accompanied or followed closely in time by the collapse of The time-series of repeat bathymetry at West Mata allows us the summit and the formation of Hades crater. It is possible to quantify the volume of eruptive products added to the volcano that the site #5 eruption was directly related to the crater with time. Figure 16 shows the recent history of cumulative

Frontiers in Marine Science | www.frontiersin.org 21 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 22

Chadwick et al. Recent Eruptions at West Mata Volcano

erupted volume at West Mata, with the volume changes from CONCLUSION individual eruptive periods plotted in the year they were discovered (that is, the year of the first subsequent ship-based The combination of nine repeated ship-based bathymetric bathymetric survey), using data from Table 2 and from Embley surveys, two high-resolution AUV surveys, and the three et al. (2014). An average linear eruption rate of ∼7.8 × 106 m3/yr expeditions that conducted ROV dives provides valuable over this time interval fits the cumulative erupted volume time- information about the recent of eruptive history at West Mata series remarkably well (Figure 16). For comparison, this is about submarine volcano since 1996. From this study we make the the volume of the 2012–2016 pillow ridge eruption on the NE following conclusions: flank of the volcano (site #3), but most of the other recent eruptions are about twice this volume (Table 2), implying an (1) The latest two ship-based bathymetric surveys in 2016 average recurrence interval of about 1–2 years between episodic and 2017 document four new eruption sites on the rift eruptions, which is relatively short. Of course, we have little ENE rift zone, on the NE flank and at the NE base of information about the eruptive activity between 1996 and 2008 – the volcano since the previous survey in 2012. AUV we only know the net volume change between the surveys at and ROV dives in November and December 2017 the beginning and the end of that period, that most of the mapped, sampled, and documented these and other volume was added at the summit and on the north flank, and recent eruption sites on the seafloor for the first time. that West Mata was in a state of continuous eruption from the (2) Early 2011 marked a change in the eruptive behavior summit near the end of that period. However, it is reasonable of West Mata, from mostly continuous summit to assume that the 1996–2008 erupted volume accumulated over activity (1996–2011) to episodic rift eruptions since a significant amount of time and that the actual cumulative then (2012–2018). eruption curve between 1996 and 2008 was probably closer to the (3) At the same time, the summit collapsed and the longer-term average rate. location of subsequent eruptions shifted from the If the recent rate of erupted volume at West Mata is summit and WSW rift zone (1996–2011) to ENE rift approximately linear, it suggests that eruptions are volume- zone (2012-present). predictable at West Mata, such that the volume of a future (4) Since 2009, there has been an episodic rift eruption eruption can be estimated simply by knowing how much every 1–2 years, spanning locations from near the time has elapsed since the previous one. It also suggests that summit to beyond the end of both rift zones at the base the magma supply is relatively steady over time, which has of the volcano, a depth range of 1200–3000 mbsl. implications for the underlying magmatic system (Wadge, 1982). (5) These eruptions have had both pyroclastic and effusive The relatively low magma supply rate (for comparison, the components, due to the high volatile content of West magma supply rate to Axial Seamount from 2011 to 2015 was Mata’s boninite magma. The proportion of tephra about an order of magnitude higher, Nooner and Chadwick, decreases with depth, with little or no tephra produced 2016) and the apparent high frequency of eruptions implies by eruptions below 2500 m. However, downslope tephra that the magma storage reservoir at West Mata must also be transport from shallower parts of the volcano by relatively small. In other words, we interpret that a steady rate turbidity currents is common. of magma is being supplied to West Mata’s shallow reservoir (6) The morphology of the recent eruption sites highly beneath the summit (at about the long-term eruption rate), but depends on the underlying slope, with shingled lava it is only 1–2 years before the pressure within the reservoir plateaus, landslide scarps, and co-eruption talus more exceeds its failure threshold and eruptions occur, which implies common on steeper slopes, and inflated lava flows with the volume of the reservoir is relatively small since it can local tumuli but lacking significant fragmental deposits only accommodate a small increase in volume before failing. on the gentler slopes at the base of the volcano. Conversely, if the reservoir volume were large, then it would be (7) The eruptions at West Mata appear to be volume- able to accommodate a small magma supply for longer before predictable with time, suggesting a constant magma eruptions are triggered by high internal pressure. Additional supply rate and a relatively small magma storage support for this conceptual model comes from the changes reservoir that can only accommodate a modest influx in the chemistry of lavas erupted between 2009 and 2011, of magma between eruptions. which are consistent with a small and frequently replenished (8) The wide range of recent eruptive sites at West Mata magma body at West Mata (Rubin et al., 2015, 2018). The provide well-documented examples of the range of apparently low strength of the magma reservoir might be related eruption styles and emplacement processes that are to the largely clastic character of the volcano. In any case, its common to basaltic submarine volcanoes worldwide. recent history implies that West Mata will likely continue to experience frequent eruptions, perhaps every few years, and therefore is an important target for continued re-mapping efforts DATA AVAILABILITY and perhaps even an ideal candidate for long-term instrumental monitoring. Thus, West Mata continues to be one of the The data presented in this study are available at the NOAA best natural laboratories in the world for the study of active National Centers for Environmental Information (ship submarine volcanism. bathymetry), the Rolling Deck to Repository (CTD data

Frontiers in Marine Science | www.frontiersin.org 22 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 23

Chadwick et al. Recent Eruptions at West Mata Volcano

and cruise reports), the IEDA Marine Geoscience Data System by the PMEL Earth-Ocean Interactions Program and the (AUV Sentry and ROV SuBastian data), and ROV video is Cooperative Institute for Marine Resources Studies (CIMRS) available on the Schmidt Ocean Institute YouTube channel. under NOAA Cooperative Agreement NA11OAR4320091 and NA15OAR4320063. Ship time on R/V Falkor and use of AUV Sentry on expedition FK171110 were supported by the Schmidt AUTHOR CONTRIBUTIONS Ocean Institute.

WC wrote the manuscript, made the figures and tables, and was co-chief scientist on the FK171110 expedition. KR was ACKNOWLEDGMENTS chief scientist on that expedition and co-directed the ROV dives described here. SM processed and analyzed ship-based We thank the Schmidt Ocean Institute for supporting expeditions and AUV-based multibeam sonar bathymetric data. SM and FK160320 and FK171110 on R/V Falkor, as well as the ship’s AB assisted with GIS data management, volume calculations, crews and the teams that operated AUV Sentry and ROV and figure preparation. TK was chief scientist on the FK160320 SuBastian, especially expedition leaders Sean Kelley (AUV expedition and collected the 2016 multibeam bathymetric survey. Sentry) and Russell Coffield (ROV SuBastian). We also thank RE helped to interpret the new results in the context of previous the science parties of ROV expeditions TN234, RR1211, and observations at West Mata. FK171110, who contributed to their success. In addition, we thank Dave Clague, Dave Caress, and Jenny Paduan at MBARI FUNDING for making the high-resolution data available from the AUV D. Allan B. dives at West Mata in 2009 and for helpful We gratefully acknowledge the funding of the NOAA Ocean comments on an early draft of the manuscript. The text was Exploration and Research (OER) Program and NOAA’s Pacific also improved by the helpful comments from the two reviewers. Marine Environmental Laboratory (PMEL) for support of the PMEL contribution number 4927. SOEST contribution science at sea and on shore. This research was supported number 10724.

REFERENCES Caplan-Auerbach, J., Dziak, R. P., Bohnenstiehl, D. R., Chadwick, W. W. Jr., and Lau, T.-K. A. (2014). Hydroacoustic investigation of submarine landslides at Acocella, V., and Neri, M. (2009). Dike propagation in volcanic edifices: overview West Mata volcano, Lau Basin. Geophys. Res. Lett. 41, 5927–5934. doi: 10.1002/ and possible developments. Tectonophysics 471, 67–77. doi: 10.1016/j.tecto. 2014GL060964 2008.10.002 Caress, D. W., and Chayes, D. N. (2016). MB-System: Mapping the Seafloor. Allen, R. W., Berry, C., Henstock, T. J., Collier, J. S., Dondin, F. J.-Y., Rietbrock, Available at: http://www.mbari.org/data/mbsystem/[Online] and software A., et al. (2018). 30 years in the life of an active submarine volcano: a time - version is v5.5 (accessed September 15, 2016). lapse bathymetry study of the Kick ’em Jenny volcano, Lesser Antilles. Geochem. Caress, D. W., Clague, D. A., Paduan, J. B., Martin, J., Dreyer, B., Chadwick, Geophys. Geosyst. 19, 715–731. doi: 10.1002/2017GC007270 W. W. Jr., et al. (2012). Repeat bathymetric surveys at 1-metre resolution of Appelgate, B., and Embley, R. W. (1992). Submarine tumuli and inflated tube-fed lava flows erupted at Axial Seamount in April 2011. Nat. Geosci. 5, 483–488. lava flows on Axial Volcano, Juan de Fuca Ridge. Bull. Volcanol. 54, 447–458. doi: 10.1038/NGEO1496 doi: 10.1007/bf00301391 Chadwick, W. W. Jr., Cashman, K. V., Embley, R. W., Matsumoto, H., Dziak, R. P., Baker, E. T., Walker, S. L., Massoth, G. J., and Resing, J. A. (2019). The NE Lau de Ronde, C. E. J., et al. (2008). Direct video and hydrophone observations of Basin: widespread and abundant hydrothermal venting in the back-arc region submarine explosive eruptions at NW Rota-1 volcano, Mariana arc. J. Geophys. behind a superfast subduction zone. Front. Mar. Sci. 6:382. doi: 10.3389/fmars. Res. 113:B08S10. doi: 10.1029/2007JB005215 2019.00382 Chadwick, W. W. Jr., Clague, D. A., Embley, R. W., Perfit, M. R., Butterfield, D. A., Baumberger, T., Lilley, M. D., Resing, J. A., Lupton, J. E., Baker, E. T., Butterfield, Caress, D. W., et al. (2013). The 1998 eruption of Axial Seamount: new insights D. A., et al. (2014). Understanding a submarine eruption through time series on submarine lava flow emplacement from high-resolution mapping. Geochem. hydrothermal plume sampling of dissolved and particulate constituents: West Geophys. Geosyst. 14, 3939–3968. doi: 10.1002/ggge20202 Mata, 2008–2012. Geochem. Geophys. Geosyst. 15, 4631–4650. doi: 10.1002/ Chadwick, W. W. Jr., Dziak, R. P., Haxel, J. H., Embley, R. W., and Matsumoto, H. 2014GC005460 (2012). Submarine landslide triggered by volcanic eruption recorded by in-situ Bevis, M., Taylor, F. W., Schutz, B. E., Recy, J., Isacks, B. L., Helu, S., et al. (1995). hydrophone. Geology 40, 51–54. doi: 10.1130/G32495.1 Geodetic observations of very rapid convergence and back-arc extension at the Chadwick, W. W. Jr., Paduan, B. P., Clague, D. A., Dreyer, B. M., Merle, S. G., Tonga arc. Nature 374, 249–251. doi: 10.1038/374249a0 Bobbitt, A. M., et al. (2016). Voluminous eruption from a zoned magma body Björnsson, A. (1985). Dynamics of crustal rifting in NE Iceland. J. Geophys. Res. 90, after an increase in supply rate at Axial Seamount. Geophys. Res. Lett. 43, 10151–10162. 12063–12070. doi: 10.1002/2016GL071327 Björnsson, A., Johnsen, G., Sigurdsson, S., Thorbergsson, G., and Tryggvason, E. Clague, D. A. (2015). Processed Near-Bottom Multibeam Sonar Data (version 2) (1979). Rifting of the plate boundary in north Iceland, 1975-1978. J. Geophys. from the Lau Back-Arc Basin Acquired with AUV D. Allan B. During the Thomas Res. 84, 3029–3038. G. Thompson Expedition TN234 (2009). Palisades, NY: Interdisciplinary Earth Bohnenstiehl, D. R., Dziak, R. P., Matsumoto, H., and Conder, J. A. (2014). Acoustic Data Alliance. doi: 10.1594/IEDA/316787 response of submarine volcanoes in the Tofua Arc and northern Lau Basin Clague, D. A., Caress, D. W., Dreyer, B. M., Lundsten, L. J., Paduan, J. B., to two great earthquakes. Geophys. J. Int. 196, 1657–1675. doi: 10.1093/gji/ Portner, R. A., et al. (2018). Geology of the Alarcon Rise, southern Gulf of ggt472 California. Geochem. Geophys. Geosyst. 19, 807–837. doi: 10.1002/2017GC00 Buck, W. R., Einarsson, P., and Brandsdottir, B. (2006). Tectonic stress and magma 7348 chamber size as controls on dike propagation: constraints from the 1975–1984 Clague, D. A., Dreyer, B. M., Paduan, J. B., Martin, J. F., Caress, D. W., Gill, J. B., Krafla rifting episode. J. Geophys. Res. 111:B12404. doi: 10.1029/2005JB003879 et al. (2014). Eruptive and tectonic history of the Endeavour Segment, Juan de

Frontiers in Marine Science | www.frontiersin.org 23 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 24

Chadwick et al. Recent Eruptions at West Mata Volcano

Fuca Ridge, based on AUV mapping data and lava flow ages. Geochem. Geophys. Palisades, NY: Interdisciplinary Earth Data Alliance. doi: 10.1594/IEDA/32 Geosyst. 15, 3364–3391. doi: 10.1002/2014GC005415 4499 Clague, D. A., Paduan, J. B., Caress, D. W., Chadwick, W. W. Jr., Saout, M. L., Merle, S. M., Chadwick, W. W. Jr., and Rubin, K. H. (2018b). Processed Gridded Dreyer, B., et al. (2017). High-resolution AUV mapping and targeted ROV Bathymetry Data from the Tonga Volcanic Arc acquired during R/V Falkor observations of three historical lava flows at Axial Seamount. Oceanography 30, Expedition FK171110 (2017). Palisades, NY: Interdisciplinary Earth Data 82–99. doi: 10.5670/oceanog.2017.426 Alliance. doi: 10.1594/IEDA/324447 Clague, D. A., Paduan, J. B., Caress, D. W., Thomas, H., Chadwick, W. W. Jr., and Morton, J. L., and Fox, C. G. (1994). “Structural setting and interaction of Merle, S. G. (2011). Volcanic morphology of West Mata Volcano, NE Lau Basin, volcanism and sedimentation at Escanaba Trough: geophysical results,” in based on high-resolution bathymetry and depth changes. Geochem. Geophys. Geologic, Hydrothermal, and Biologic Studies at Escanaba Trough, Gorda Ridge, Geosyst. 12:QOAF03. doi: 10.1029/2011GC003791 Offshore Northern California, eds J. L. Morton, R. A. Zierenberg, and C. A. Reiss Crisp, J. A. (1984). Rates of magma emplacement and volcanic output. (Virginia, VA: United States Geological Survey), 21–44. J. Volcanol. Geotherm. Res. 20, 177–211. doi: 10.1016/0377-0273(84) Neal, C. A., Brantley, S. R., Antolik, L., Babb, J. L., Burgess, M., Calles, K., et al. 90039-8 (2019). The 2018 rift eruption and summit collapse of Kilauea Volcano. Science Deardorff, N. D., Cashman, K. V., and Chadwick, W. W. Jr. (2011). Observations of 363, 367–374. doi: 10.1126/science.aav7046 eruptive plumes and pyroclastic deposits from submarine explosive eruptions Nooner, S. L., and Chadwick, W. W. Jr. (2016). Inflation-predictable behavior at NW Rota-1. Mariana Arc. J. Volcanol. Geothermal Res. 202, 47–59. doi: and co-eruption deformation at Axial Seamount. Science 354, 1399–1403. doi: 10.1016/j.jvolgeores.2011.01.003 10.1126/science.aah4666 Denlinger, R. P., and Holmes, M. L. (1994). “A thermal and mechanical model Resing, J. A., Rubin, K. H., Embley, R. W., Lupton, J. E., Baker, E. T., for sediment hills and associated sulfide deposits along escanaba trough,” in Dziak, R. P., et al. (2011). Active submarine eruption of boninite in Geologic, Hydrothermal, and Biologic Studies at Escanaba Trough, Gorda Ridge, the northeastern Lau Basin. Nat. Geosci. 4, 799–806. doi: 10.1038/NGEO Offshore Northern California, eds J. L. Morton, R. A. Zierenberg, and C. A. Reiss 1275 (Virginia, VA: U.S. Geological Survey), 65–75. Rubin, K. H., Chadwick, W. W. Jr., Embley, R. W., Merle, S. G., Shank, T. M., Deschamps, A., Grigné, C., Le Saout, M., Soule, S. A., Allemand, P., Van Vliet Cho, W., et al. (2018). “Exploration of the Mata Submarine Volcano Group Lanoe, B., et al. (2014). Morphology and dynamics of inflated subaqueous Reveals Volcano-Tectonic-Hydrothermal Links,”in Abstract V14A-08 presented basaltic lava flows. Geochem. Geophys. Geosyst. 15, 2128–2150. doi: 10.1002/ at 2018 Fall Meeting (Washington, DC: AGU). 2014GC005274 Rubin, K. H., Michael, P., Jenner, F., Clague, D., Glancy, S., Hellebrand, E., Dziak, R. P., Bohnenstiehl, D. R., Baker, E. T., Matsumoto, H., Caplan-Auerbach, et al. (2015). “Composition within and between Tonga arc/Lau Basin J., Embley, R. W., et al. (2015). Long-term explosive degassing and debris flow backarc eruptions reveal wide variety of parent melts linked to activity at West Mata submarine volcano. Geophys. Res. Lett. 42, 1480–1487. eruption styles,” in Proceedings of the Goldschmidt Conference Abstracts, doi: 10.1002/2014GL062603 Prague. Embley, R. W., Chadwick, W. W. Jr., Baker, E. T., Butterfield, D. A., Resing, Rubin, K. H., Soule, S. A., Chadwick, W. W. Jr., Fornari, D. J., Clague, D. A., J. A., De Ronde, C. E. J., et al. (2006). Long-term eruptive activity Embley, R. W., et al. (2012). Volcanic eruptions in the deep sea. Oceanography at a submarine arc volcano. Nature 441, 494–497. doi: 10.1038/nature 25, 142–157. doi: 10.5670/oceanog.2012.12 04762 Schnur, S. R., Chadwick, W. W. Jr., Embley, R. W., Ferrini, V. L., De Ronde, Embley, R. W., Merle, S. G., Baker, E. T., Rubin, K. H., Lupton, J. E., Resing, J. A., C. E. J., Cashman, K. V., et al. (2017). A decade of volcanic construction and et al. (2014). Eruptive modes and hiatus of volcanism at West Mata seamount, destruction at the summit of NW Rota-1 seamount: 2004–2014. J. Geophys. Res. NE Lau Basin: 1996-2012. Geochem. Geophys. Geosyst. 15, 4093–4115. doi: 122, 1558–1584. doi: 10.1002/2016JB013742 10.1002/2014GC005387 Soule, S. A., Fornari, D. J., Perfit, M. R., and Rubin, K. H. (2007). New insights into Embley, R. W., and Rubin, K. H. (2018). Extensive young silicic volcanism mid-ocean ridge volcanic processes from the 2005–2006 eruption of the East produces large deep submarine lava flows in the NE Lau Basin. Bull. Volcanol. Pacific Rise, 9◦46’N–9◦56’N. Geology 35, 1079–1082. 80:36. Staudigel, H., Hart, S. R., Pile, A., Bailey, B. E., Baker, E. T., Brooke, S., et al. Fornari, D. J., Tivey, M. A., Schouten, H., Perfit, M., Yoerger, D., Bradley, A., (2006). Vailulu’u Seamount, Samoa: Life and death on an active submarine et al. (2004). “Submarine lava flow emplacement at the East Pacific Rise volcano. Proc. Natl. Acad. Sci. U.S.A. 103, 6448–6453. doi: 10.1073/pnas.060083 9◦50’N: Implications for uppermost ocean crust stratigraphy and hydrothermal 0103 fluid circulation,” in Mid-Ocean Ridges: Hydrothermal Interactions Between Wadge, G. (1982). Steady state volcanism: evidence from eruption histories of the Lithosphere and Oceans, eds C. R. German, J. Lin, and L. M. Parson polygenetic volcanoes. J. Geophys. Res. 87, 4035–4049. (Washington, DC: American Geophysical Union), 187–217. doi: 10.1029/ Walker, G. P. L. (1991). Structure, and origin by injection of lava under 148gm08 surface crust, of tumuli, "lava rises", "lava-rise pits", and "lava-inflation Fundis, A. T., Soule, S. A., Fornari, D. J., and Perfit, M. R. (2010). Paving the clefts" in Hawaii. Bull. Volcanol. 53, 546–558. doi: 10.1007/bf0029 seafloor: volcanic emplacement processes during the 2005-2006 eruptions at the 8155 fast spreading East Pacific Rise, 9◦50’N. Geochem. Geophys. Geosyst. 11:Q08024. Watts, A. B., Peirce, C., Grevemeyer, I., Pauletto, M., Stratford, W. R., Bassett, doi: 10.1029/2010GC003058 D., et al. (2012). Rapid rates of growth and collapse of Monowai submarine Haymon, R. M., White, S. M., Baker, E. T., Anderson, P. G., Macdonald, K. C., volcano in the Kermadec Arc. Nat. Geosci. 5, 510–515. doi: 10.1038/ngeo1473 and Resing, J. A. (2008). High-resolution surveys along the hot spot – affected doi: 10.1038/ngeo1473 Galapagos Spreading Center: 3. Black smoker discoveries and the implications White, S. M., Macdonald, K. C., and Haymon, R. M. (2000). Basaltic lava domes, for geological controls on hydrothermal activity. Geochem. Geophys. Geosyst. lava lakes, and volcanic segmentation on the southern East Pacific Rise. 9:Q12006. J. Geophys. Res. 103, 25519–25536. Klein, E. M., White, S. M., Nunnery, J. A., Mason-Stack, J. L., Wanless, V. D., Perfit, White, S. M., Macdonald, K. C., and Sinton, J. M. (2002). Volcanic mound M. R., et al. (2013). Seafloor photo-geology and sonar terrain modeling at the fields on the East Pacific Rise, 16◦-19◦S: low effusion rate eruptions 9◦N overlapping spreading center, East Pacific Rise. Geochem. Geophys. Geosyst. at overlapping spreading centers for the past 1 Myr. J. Geophys. Res. 14, 5146–5170. doi: 10.1002/2013GC004858 107:2240. McClinton, T., White, S. M., Colman, A., and Sinton, J. M. (2013). Reconstructing White, S. M., Meyer, J. D., Haymon, R. M., Macdonald, K. C., Baker, E. T., and lava flow emplacement processes at the hotspot-affected Galapagos Spreading Resing, J. A. (2008). High-resolution surveys along the hot spot – affected Center, 95◦W and 92◦W. Geochem. Geophys. Geosyst. 14, 2731–2756. doi: 10. Galapagos Spreading Center: 2. Influence of magma supply on volcanic 1002/ggge.20157 morphology. Geochem. Geophys. Geosyst. 9:Q09004. Merle, S., Chadwick, W., and Rubin, K. (2018a). Processed Gridded Near- Wilcock, W. S. D., Dziak, R. P., Tolstoy, M., Chadwick, W. W. Jr., Nooner, Bottom AUV Sentry Bathymetric Sonar Data (NetCDF:GMT format) from S. L., Bohnenstiehl, D. R., et al. (2018). The recent volcanic history of Axial the NE Lau Basin Acquired During Falkor Expedition FK171110 (2017). Seamount: geophysical insights into past eruption dynamics with an eye toward

Frontiers in Marine Science | www.frontiersin.org 24 August 2019 | Volume 6 | Article 495 fmars-06-00495 August 16, 2019 Time: 18:14 # 25

Chadwick et al. Recent Eruptions at West Mata Volcano

enhanced observations of future eruptions. Oceanography 31, 114–123. doi: Conflict of Interest Statement: The authors declare that the research was 10.5670/oceanog.2018.117 conducted in the absence of any commercial or financial relationships that could Yeo, I. A., Clague, D. A., Martin, J. F., Paduan, J. B., and Caress, D. W. (2013). be construed as a potential conflict of interest. Preeruptive flow focussing in dikes feeding historical pillow ridges on the Juan de Fuca and Gorda Ridges. Geochem. Geophys. Geosyst. 14, 3586–3599. Copyright © 2019 Chadwick, Rubin, Merle, Bobbitt, Kwasnitschka and Embley. doi: 10.1002/ggge.20210 This is an open-access article distributed under the terms of the Creative Commons Zellmer, K. E., and Taylor, B. (2001). A three-plate kinematic model for Lau Basin Attribution License (CC BY). The use, distribution or reproduction in other forums opening. Geochem. Geophys. Geosyst. 2, 1–26. doi: 10.1029/2000GC000106 is permitted, provided the original author(s) and the copyright owner(s) are credited Zierenberg, R. A., Clague, D. A., Paduan, J. B., and Caress, D. W. (2013). New maps and that the original publication in this journal is cited, in accordance with accepted focus 30-odd years of investigation of the Escanaba Trough spreading center. academic practice. No use, distribution or reproduction is permitted which does not Geol. Soc. Am. Abstr. Programs 47:381. comply with these terms.

Frontiers in Marine Science | www.frontiersin.org 25 August 2019 | Volume 6 | Article 495